From (2), the angular frequencies of harmonic current in field
windings are h-1 or h+1 times as same as that of fundamental
currents because the frequency of induced filed current equals to
that of d-q currents. So odd-order harmonic currents in power
system can be compensated by ejecting even-order harmonic
currents into field windings of synchronous machine, which is
identical with conclusions in [6] and [7].